438 NERVOUS SYSTEM, 



toid process, and is inserted tendinous into the convex side of 

 the concha near the meatus auditorius. 

 It draws the pinna backwards. 



3. The Anterior Auricula? is a small quadrangular slip, just 

 above the root of the zygomatic process. It arises from the 

 temporal fascia, and is inserted tendinous into the fore part of 

 the helix just above its beginning. 



It draws the pinna forwards and upwards. 



. SECT. II. OF THE TYMPANUM. 



The Tympanum is the middle portion of the organ of hear- 

 ing, being interposed between the meatus auditorius and the 

 labyrinth. Its depth is about three lines, its antero-posterior 

 diameter about six, and its vertical diameter rather more, though 

 from the general inequality of the cavity, and its communication 

 with adjoining cavities, it is not easy to fix upon very precise 

 measurements. 



The Membrana Tympani. is a complete membranous septum, 

 interposed between the meatus externus and the tympanum. It 

 is placed very obliquely, so that its upper edge inclines outwards, 

 and its under edge inwards; the latter, therefore, forms a very 

 acute entering angle with the inferior part or floor of the meatus^ 

 and gives to that portion of the meatus an additional length, 

 which renders it difficult to see to its bottom. The membrane 

 of the tympanum is nearly circular, and has its circumference 

 adhering very closely to the external orifice of the tympanum. 

 It is slightly tense, and has its middle drawn inwards by being 

 attached to the handle of the malleus. 



The membrani tympani consists of four laminae; the two ex- 

 terior of which, being the cuticle and the cutis vera, which line 

 the meatus auditorius, are easily detached, as mentioned be- 

 fore, and seem scarcely to adhere to the layer below. The 

 third layer is the proper membrane, and is distinguished by its 

 dryness and by its transparency. Sir Everard Home was ena- 

 bled to detect radiated muscular fibres, forming it in the ele- 

 phant.* In the human, subject, its fibrous character is best seen 



* PhilosophicalTransactions, for 1800. London. 



